package com.appleyk.utils;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

/**
 * <p>
 * 名称：IdWorker.java
 * </p>
 * <p>
 * 描述：分布式自增长ID
 * </p>
 * 
 * <pre>
 *     Twitter的 Snowflake　JAVA实现方案
 * </pre>
 * 
 * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用： 1||0---0000000000
 * 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
 * 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，
 * 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），
 * 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。
 * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），
 * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。
 * <p>
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 *
 * @author Polim
 */
public class IdsMaker {
	/**
	 * 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
 	 */
	private final static long TWEPOCH = 1288834974657L;
    /**
     * 机器标识位数
     */
	private final static long WORKER_ID_BITS = 5L;
    /**
     * 数据中心标识位数
     */
	private final static long DATACENTER_ID_BITS = 5L;
    /**
     * 机器ID最大值
     */
	private final static long MAX_WORKER_ID = -1L ^ (-1L << WORKER_ID_BITS);
    /**
     * 数据中心ID最大值
     */
	private final static long MAX_DATACENTER_ID = -1L ^ (-1L << DATACENTER_ID_BITS);
    /**
     * 毫秒内自增位
     */
	private final static long SEQUENCE_BITS = 12L;
    /**
     * 机器ID偏左移12位
     */
	private final static long WORKER_ID_SHIFT = SEQUENCE_BITS;
    /**
     * 数据中心ID左移17位
     */
	private final static long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    /**
     * 时间毫秒左移22位
     */
	private final static long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    /**
     *
     */
	private final static long SEQUENCE_MASK = -1L ^ (-1L << SEQUENCE_BITS);
    /**
     * 上次生产id时间戳
     */
	private static long lastTimestamp = -1L;
    /**
     * 0，并发控制
     */
	private long sequence = 0L;

	private final long workerId;
    /**
     * 数据标识id部分
     */
	private final long datacenterId;

	public IdsMaker() {
		this.datacenterId = getDatacenterId(MAX_DATACENTER_ID);
		this.workerId = getMaxWorkerId(datacenterId, MAX_WORKER_ID);
	}

	/**
	 * @param workerId
	 *            工作机器ID
	 * @param datacenterId
	 *            序列号
	 */
	public IdsMaker(long workerId, long datacenterId) {
		if (workerId > MAX_WORKER_ID || workerId < 0) {
			throw new IllegalArgumentException(
					String.format("worker Id can't be greater than %d or less than 0", MAX_WORKER_ID));
		}
		if (datacenterId > MAX_DATACENTER_ID || datacenterId < 0) {
			throw new IllegalArgumentException(
					String.format("datacenter Id can't be greater than %d or less than 0", MAX_DATACENTER_ID));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}

	/**
	 * 获取下一个ID
	 *
	 * @return
	 */
	public synchronized long nextId() {
		long timestamp = timeGen();
		if (timestamp < lastTimestamp) {
			throw new RuntimeException(String.format(
					"Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
		}

		if (lastTimestamp == timestamp) {
			// 当前毫秒内，则+1
			sequence = (sequence + 1) & SEQUENCE_MASK;
			if (sequence == 0) {
				// 当前毫秒内计数满了，则等待下一秒
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			sequence = 0L;
		}
		lastTimestamp = timestamp;
		// ID偏移组合生成最终的ID，并返回ID
		long nextId = ((timestamp - TWEPOCH) << TIMESTAMP_LEFT_SHIFT) | (datacenterId << DATACENTER_ID_SHIFT)
				| (workerId << WORKER_ID_SHIFT) | sequence;

		String id = String.valueOf(nextId);
		id = id.substring(6, id.length());
		nextId = Long.parseLong(id);
		return nextId;
	}

	private long tilNextMillis(final long lastTimestamp) {
		long timestamp = this.timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = this.timeGen();
		}
		return timestamp;
	}

	private long timeGen() {
		return System.currentTimeMillis();
	}

	/**
	 * <p>
	 * 获取 MAX_WORKER_ID
	 * </p>
	 */
	protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
		StringBuffer mpid = new StringBuffer();
		mpid.append(datacenterId);
		String name = ManagementFactory.getRuntimeMXBean().getName();
		if (!name.isEmpty()) {
			/*
			 * GET jvmPid
			 */
			mpid.append(name.split("@")[0]);
		}
		/*
		 * MAC + PID 的 hashcode 获取16个低位
		 */
		return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
	}

	/**
	 * <p>
	 * 数据标识id部分
	 * </p>
	 */
	protected static long getDatacenterId(long maxDatacenterId) {
		long id = 0L;
		try {
			InetAddress ip = InetAddress.getLocalHost();
			NetworkInterface network = NetworkInterface.getByInetAddress(ip);
			if (network == null) {
				id = 1L;
			} else {
				byte[] mac = network.getHardwareAddress();
				id = ((0x000000FF & (long) mac[mac.length - 1])
						| (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
				id = id % (maxDatacenterId + 1);
			}
		} catch (Exception e) {
			System.out.println(" getDatacenterId: " + e.getMessage());
		}
		return id;
	}
}